The present invention relates to optical microphones, and more particularly to an echo-cancelling system for optical microphones.
U.S. Pat. No. 5,771,091 discloses an optical microphone/sensor including a source of light for producing light used in sensing measurements, which light is transmitted to a reflective membrane either directly from the source or through an optical guide, e.g., an optical fiber or a solid body. Light reflected from the membrane is propagated to a photodetector, either directly or through another light guide. Output signals from the photodetector are proportional to the intensity of the reflected light.
As is experienced by many, echoes emanating from a nearby loudspeaker or other source present disturbances and impair quality communication.
It is therefore a broad object of the present invention to provide an optical microphone system which substantially eliminates echo signals in communication systems to which it is connected, thereby improving the quality of communications.
The invention thus provides an echo-cancelling system for an optical microphone, for eliminating acoustical echoes from a source of acoustical signals to which the microphone is connected, the system comprising a source of light for illuminating the acoustical membrane; a photodetector for receiving light reflected from said membrane and for producing output signals; means for supplying power to said source of light; a preamplifier for amplifying said output signals; an input terminal for receiving electrical signals from said source of acoustical signals; a time delay circuit for receiving signals from said source of acoustical signals, and a circuit system for regulating the amplitude of the delayed electrical signals, connected between said delay circuit and said source of light, for changing the current supplied to said source of light by said light source power means.